The present invention relates to a power control apparatus for a motor assisted turbo charger and also relates to a motor driven turbo charging apparatus.
There is a conventional turbo charger including an induction motor, which is hereinafter referred to as a motor-equipped turbo charger. The induction motor assists the turbo charger to rotate its rotary shaft with better response so that the turbo charger can speedily increase the rotational speed (for example, as disclosed in the U.S. Pat. No. 6,449,950 or in the International Publication No. 02/23047).
For example, the motor-equipped turbo charger operates in a very wide rotational speed region ranging from a low speed region (e.g. 1×104 rpm to 2×104 rpm) corresponding to an engine idling condition to an ultra-high speed region (e.g. approximately 20×104 rpm) corresponding to an engine full load condition. The motor-equipped turbo charger is thus required to quickly increase its rotational speed within a short time (e.g. approximately 1 sec.) so as to operate in such a very wide rotational speed region. The rotational speed of 20×104 rpm (referred to as the ultra-high speed region in this invention) corresponds to 10 times to 100 times the rotational speed of a conventional motor installed on a vehicle. Such severe operating conditions force the motor-equipped turbo charger to encounter with later-described power control problems.
To attain high response required for rapidly increasing the rotational speed in a short time, the motor-equipped turbo charger needs to generate a very large output torque and accordingly a very large amount of electric power must be supplied to the motor of the turbo charger. According to a car of 2,000 CC displacement, the electric power level required for a motor of the turbo charger to attain the above-described performances is 1.5 kW to 5.6 kW (for example, refer to “Trend of Variable Turbochargers: VGT, VNT” by Hiroshi UCHIDA, Engine Technology, Vol. 5, No. 1, February 2003, p. 20 to p. 25).